Prevulcanization of rubbers by hydrogen peroxide and an activator

ABSTRACT

A prevulcanized polymer latex is made by treating an unsaturated polymer in an aqueous medium with hydrogen peroxide and a hydrogen peroxide activator which does not encourage the decomposition of the hydrogen peroxide to produce molecular oxygen under the conditions of the treatment. The prevulcanized polymer latex may be used in latex applications such as in adhesives, coatings, carpet backings, dips, threads, tapes and foams, of which the following is a Specification.

United States Patent Rodaway et al.

[ 1 Aug. 28, 1973 PREVULCANIZATION OF RUBBERS BY HYDROGEN PEROXIDE ANDAN ACTIVATOR [75] Inventors: Bruce K. Rodaway, Erdington,

Birmingham; Kenneth O. Calvert, Sutton Coldfield, both of England [73]Assignee: Dunlop Holdings Limited, London,

England [22] Filed: Sept. 8, 1970 [21] Appl. No.: 70,584

[30] Foreign Application Priority Data Sept. 12, 1969 Great Britain45,017/69 Apr. 29, 1970 Great Britain 20,499/70 [52] 0.8. Cl. 260/29.7AT, 260/83.3, 260/85.1, 260/94.7 A, 260/96 R [51] Int. Cl...... C08d7/00, C08d 13/28, C08f 1/88, C08f 27/00 [58] Field of Search 260/29.7AT, 29.7 EM, 260/833, 85.1, 96 R, 94.7 A

[56] References Cited UNITED STATES PATENTS 2,447,772 8/1948 Rust et al.260/29.7 AT

3/1966 Floyd 26009.7 AT 3/1960 Canterino et a] 260/29.7 AT

OTHER PUBLXCATIONS Ephraim, Inorganic Chemistry" 4 Ed. Rev., pp.410-514-518, 843 (Nordeman, 1943).

Primary ExaminerMorris Liebman Assistant ExaminerP. N. Thomas, Jr.Attorney-Stevens, Davis, Miller & Mosher 14 Claims, No DrawingsPREVULCANIZATION OF RUBBERS BY HYDROGEN PEROXIDE AND AN ACTIVATOR Thisinvention relates to the production of prevulcanized polymer latices.

According to the present invention a method for the production of aprevulcanized polymer latex comprises treating an unsaturated polymer inan aqueous medium with hydrogen peroxide together with a hydrogenperoxide activator which does not encourage the decomposition of thehydrogen peroxide to produce molecular oxygen under the conditions ofthe treatment.

According to the present invention also there is provided aprevulcanized polymer latex when prepared by the method described in theimmediately preceding paragraph.

By the term prevulcanized polymer latex there is meant a latex in whichthe polymer particles have been vulcanized and from which vulcanizedfilms can be produced merely by drying.

The hydrogen peroxide may be conveniently employed as an aqueoussolution of concentration 5 to 65 per cent by mass, e.g. 30 per cent bymass (100-volume hydrogen peroxide).

The activator may be an inorganic compound which yields a per-acid orper-salt by reaction with hydrogen peroxide in aqueous medium. Forexample, it may be an acidic or amphoteric inorganic oxide or a saltthereof. Examples of such activators are sodium and potassium salts suchas the molybdates, tungstates, stannates, borates, pervanadates,metasilicates (preferably in conjunction with potassium hydroxide),aluminates and bicarbonates, lithium chloride and boric acid. Theactivator is suitably added to the unsaturated polymer as an aqueoussolution or dispersion. The amount of such an activator employed may beas little as one millimole per mole of hydrogen peroxide. In someinstances no activator need be added since the unvulcanized polymerlatex may contain such an activator owing to its method of preparation.

Alternatively, the activator may be an organic compound which yields aper-acid or per-salt by reaction with hydrogen peroxide in aqueousmedium. Examples of such an activator are formic acid, formaldehyde, andfluoroacetic acid. Such an activator may be conveniently formed in situbut may alternatively be preformed if desired. For example, perforrnicacid may be formed by the reaction of fonnaldehyde with hydrogenperoxide, preferably in the molar ratio 1:2. The peracid so formed ispresent as one component of an equilibrium system comprising water,hydrogen peroxide, organic acid and organic per-acid.

The treatment of the unsaturated polymer may take place in air and mayconveniently be performed at room temperature. Preferably the reactionis performed under conditions which minimise loss of oxygen. Forexample, when the treatment is performed on a natural rubber latex ithas been found advantageous to include a small quantity (e.g. about 0.1percent based on the polymer) of a metal ion complexing agent such asthe disodium salt of ethylenediamine tetraacetic acid. This is tosequester the metal ions such as copper and manganese ions present inthe latex which would otherwise cause the rapid decomposition of thehydrogen peroxide to molecular oxygen. This approach may be usedwhenever excessive foaming, which may be attributed to the presence ofundesirable metallic contaminants, is encountered. Further, when anorganic activator is employed the reaction is preferably performed underacidic conditions in order to minimise the decomposition of hydrogenperoxide to molecular oxygen.

Unsaturated polymers which may be treated by the method of thisinvention may suitably be rubbers, and examples of unsaturated polymerswhich may be treated are styrene/butadiene copolymers, ethylene/-propylene/diene terpolymers, polybutadiene, polychloroprene,styrene/butadiene/vinylpyridine terpolymers, butadiene/acrylonitrilecopolymers, isoprene/acrylonitrile copolymers, carboxylatedstyrene/butadiene copolymers and natural rubber.

Useful prevulcanized latices may be prepared by blending two or moreunsaturated polymers together before or after treatment of at least oneof the polymers by the method of the present invention. For example, oneunsaturated polymer, e.g. a styrene/butadiene rubber, may be treated bythe method of this invention and then blended with another unsaturatedpolymer, e.g. natural rubber. Alternatively a blend of two unsaturatedpolymers, e.g. styrene/butadiene rubber and natural rubber, may betreated by the method of this invention.

If desired, the prevulcanized polymer latices pr0- duced by the methodof this invention may be formed by any of the usual techniques. Forexample, foaming may be achieved by means of hydrogen peroxide which istreated to liberate oxygen e.g. by means of an enzyme catalyst (Talalayprocess), or by a mechanical foaming technique.

The polymer latices treated according to this invention are found tohave the properties of prevulcanized polymers latices. Moreover, it isfound that prevulcanized polymer latices, especially foams, are capableof containing a very high proportion of a filler material withoutserious detriment to resiliency. The prevulcanized polymer latices oftenhave enhanced strength properties and good compatibility with untreatedlatices.

If desired, the prevulcanized polymer latices may be further vulcanizedby the use of conventional sulphurcontaining vulcanizing ingredientse.g. sulphur itself. Also, the prevulcanized polymer latices may bereacted with reactive compounds such as isocyanates and aldehyde resinse.g. resorcinol/formaldehyde resins, if de- EXAMPLE I 1 litre of a 68percent total solids latex of a styrene/- butadiene rubber containing 25percent styrene by mass (trade name lntex was mixed with two parts byweight of sodium lauryl sulphate and two parts by weight of Pluronic F68(a condensate of ethylene oxide and a hydrophobic base produced bycondensing propylene oxide and propylene glycol, available fromWyandotte Chemicals Corp.) per 100 parts by weight of rubber, and 60 mlof 100-volume hydrogen peroxide together with 0.5 g of potassiummolybdate as a 5 percent aqueous solution were added. After about fourhours at room temperature (about 20 C.) the resulting prevulcanizedpolymer latex was compounded as shown in Table 1.

TABLE 1 Part(s) by weight (wet) Prevulcanized polymer latex 200 50%Aqueous zinc oxide 6 50% Aqueous zinc diethyldithio-carbamate(antioxidant) 1 MS 200 Silicone oil 0.7 50% Aqueous Trimene base (foamstabilizer) 2 Aluminium silicate 100 (dry) Trimene base is a reactionproduct of ethyl chloride, formaldehyde and ammonia. The compoundedpolymer latex was foamed mechanically and 4 ml of a 20 percent aqueousammonium acetate (heat-gelling agent) solution were stirred in. The foamwas spread on a hessian sheet to a depth of 1 cm and was gelled byheating with infra-red radiation. After drying at room temperature(about 20 C.) the foam showed good recovery from indentation. In fact,even when wet, the foam could be cut with scissors without any permanentdeformation of the cut edge.

EXAMPLE 11 100 g portions of a 68 percent total solids latex of astyrene/butadiene rubber containing 25 percent styrene by mass (tradename lntex 100) were treated with 0.05 g of potassium molybdate and 0,2, 4, 6, 8 or 10 ml of 100-volume hydrogen peroxide at room temperature(about 25 C.). When the reaction was complete, as judged by thedisappearance of the pink coloration of the latex caused by the presenceof the perrnolybdic salt, a film of each latex about 0.5 mm deep wasspread on a glass plate. The films were dried in air at room temperatureuntil clear. A weighed portion of each film was then swollen in tolueneat 30 C. for 24 hours. The swollen films were weighed and the volumeswelling and cross-link density calculated. The results of these testsare given in Table I].

TABLE 11 volume Cross-link Density experiment ml 11,0, swelling M,-- X10 No. l Dissolved 2 2 partially dissolved 3 4 17.65 0.17 4 6 15.70 0.208 13.45 0.27 6 10 10.79 0.39

EXAMPLE 111 T0100 g portions of a 68 percent total solids latex of astyrene/butadiene rubber containing 25 percent styrene by mass (tradename Intex 100), stabilized with three parts by weight of sodium laurylsulphate per 100 parts by weight of rubber, were added hydrogen peroxideand formaldehyde in the molar ratio 2:1 in the ene at 30 C. for 24hours. The swollen films were weighed and the volume swelling andcross-link density calculated. The results of these tests are given inTable 111.

TABLE 111 experml 10M ml 10M volume cross-link density iment H O, CH,Oswelling M X 10" No. 7 0 0 dissolved 8 12 6 17.57 0.17 9 16 8 14.17 0.2410 2O 10 13.54 0.26

The films prepared from the prevulcanized latices of Examples 11 and 111were rubbery and showed a considerable improvement in strength andresilience over similar films cast from the untreated latex.

EXAMPLE IV A styrene/butadiene rubber containing 25 percent styrene bymass, in the form of a 10 percent solution in toluene, was treated withhydrogen peroxide and activator in the proportions of Experiment No. 4in Example 11 and Experiment No. 9 in Example 111. There was no evidenceof cross-linking in the polymer solution, i.e., the solution did not geland the polymer recovered by evaporation of the solvent showed noobvious difference from the polymer recovered from an untreatedsolution.

EXAMPLE V To 18 litres of a 68 percent total solids latex of astyrene/butadiene rubber containing 25 percent styrene by mass (tradename lntex contained in a stainless steel reaction vessel jacketted at16 C, were added 9 g of sodium tungstate (as a 5 percent aqueoussolution) and 1,080 ml of 100-volume hydrogen peroxide. The mixture wasgently stirred for 24 hours while the reaction proceeded. One part byweight of potassium oleate per 100 parts by weight of rubber was addedto the resulting prevulcanized latex.

A film about 1.5 mm thick was prepared from the latex by casting it in astainless steel mould and drying in air a room temperature. Threetest-pieces from the dried film were tested at a rate of elongation of50 cm per minute'after conditioning for a minimum of 24 hours in anatmosphere of controlled temperature and humidity. Three test-piecesfrom the untreated latex were prepared and tested in identical manner.The results of these tests are given in Table IV.

TABLE IV Prevulcanized Untreated latex latex Modulus (k cm) at extension0 100% 7.1 6.2 300% 8.9 3.9 500% 10.9 Elongation-at-break (9b) 530 330Tensile strength (kg/cm) 11.6 6.2

The test-pieces from the untreated latex started to flow plastically at100 percent elongation and yielded at the elongation-at-break quoted,whereas the test pieces from the prevulcanized latex did not flowplastically and snapped at the elongation-at-break stated.

EXAMPLE V1 One litre of a 65 percent total solids latex of a reinforcedstyrene/butadiene rubber containing 36 percent styrene by mass wastreated with 10 ml of 5 percent sodium tungstate solution and 60 ml of100-volume hydrogen peroxide at room temperature (about 20 C). Ten dayslater dried films were prepared from both the resulting prevulcanizedlatex and the untreated latex and tested as in Example V. The results ofthese tests are given in Table V.

TABLE V Prevulcanized Untreated latex latex Modulus (k cm) at extension100% 6 10 300% 8 7 500% 1 1 Elongation-at-break (56) l 150 I 100 TensileStrength (kg/cm) 59 10 The test-pieces from the untreated latex startedto flow plastically at about 100 percent elongation and subsequentlyyielded, whereas the test-pieces from the prevulcanized latex did notflow plastically and snapped at the elongation-at-break stated.

EXAMPLE VII To illustrate that the prevulcanized latex may be furthervulcanized by the use of conventional sulphurcontaining vulcanizingingredients, the prevulcanized latex of Example VI was compounded asshown in Table VI.

TABLE VI Trimene base is a reaction product of ethyl chloride,formaldehyde and ammonia.

The ingredients were added as aqueous dispersions or solutions. Thefigure given in brackets after the ingredient indicates the proportionby weight of dry ingredient in the dispersion or solution.

The compounded latex was diluted to 30 percent polymer content and castinto a stainless steel mould about 1.5 mm deep. The mould was placed insteam at 100 C for 2 minutes to gel the compounded latex. The gelledfilm was leached in running water, dried at room temperature and heatedin steam at 100 C for 10 minutes. The resulting film was tested as inExample V and the results are given in Table VII.

The untreated latex of Example VI was also compounded to the formulationgiven in Table VI and a dried, gelled film was prepared in the samemanner as for the prevulanized latex. This film was heated in steam at100 C for 90 minutes (the time required to obtain maximum tensilestrength). The resulting film was tested as in Example V and the resultsare given in Table VII.

TABLE VII Prevulcanized Untreated latex latex Tensile strength (kg/cm)125 66 Elongation-atbreak (96) 730 5 10 EXAMPLE VIII Two litres of a 31percent total solids latex of a styrene/butadiene rubber containing 25percent styrene by mass (trade name Intex F28) were treated with 10 mlof 5 percent sodium tungstate solution and 55 ml of l00-volume hydrogenperoxide at room temperature (about 20 C). Five days later the pH of theresulting prevulcanized latex was adjusted to 9.7 by the addition of 10percent potassium hydroxide solution. Dried films were prepared fromboth the prevulcanized latex and the untreated latex and tested as inExample V. The results of these tests are given in Table VIII.

TABLE VIII Prevulcanized Untreated latex latex Modulus (kg/cm) atextension of: 100% 5 6 300% 7 8 500% 9 Elongation-at-break (36) 880 410Tensile strength (kg/cm) 23 9 EXAMPLE IX 500 g of a polybutadiene latexcontaining 58 percent total solids (trade name Polysar Latex 710) weretreated with 5 ml of 5 percent sodium tungstate solution and 25 ml of100-volume hydrogen peroxide at room temperature (about 20 C). Four dayslater dried films were prepared from both the resulting prevulcanizedlatex and the untreated latex and tested as in Example V.

The test-pieces from the untreated latex flowed during extension andyielded at an elongation of about 500 percent, whereas the test-piecesfrom the prevulcanized latex did not flow and broke with a tensilestrength of 10 kg/cm at an elongation of 890 percent.

EXAMPLE X 500 g of a polychloroprene latex containing 58 percent totalsolids (trade name Neoprene Latex 650) were treated with 4' ml of 5percent sodium tungstate solution and 12.5 ml of l00-volume hydrogenperoxide at room temperature (about 20 C), Two days later dried filmswere prepared from both the resulting prevulcanized latex and theuntreated latex and tested as in Example V. The results of these testsare given in Table IX.

TABLE IX Prevulcanized Untreated latex latex Modulus (kg/cm) atextension of: 100% 9 9 300% l 3 I3 500% 23 25 EIongation-at-break 920640 Tensile strength (kg/cm) 91 36 EXAMPLE XI 500 g of avinylpyridine/styrene/butadiene terpolymer latex containing 41 percenttotal solids (trade name Dunlop Vinyl Pyridine Latex) were treated with3 ml of 5 percent sodium tungstate solution and 10 ml of l00-volumehydrogen peroxide at room temperature (about 20 C). Two days later driedfilms were pre pared from both the resulting prevulcanized latex and theuntreated latex and tested as in Example V.

The test-pieces from the untreated latex yielded at an elongation of 850percent with a tensile strength of only 2 kg/cm whereas the test-piecesfrom the prevulcanized latex broke at an elongation of 1,075 percentwith a tensile strength of 7 kg/cm EXAMPLE XII One litre of a 62 percenttotal solids latex of a butadiene/acrylonitrile rubber containing 34percent acrylonitrile by mass (trade name Polysar Latex 762) was treatedwith 5 ml of 20 percent potassium hydroxide solution, 10 ml of 5 percentsodium tungstate solution and 40 ml of lOO-volume hydrogen peroxide atroom temperature (about 20 C). Two weeks later dried films were preparedfrom both the prevulcanized latex and the untreated latex. The driedfilms were heated in steam at 100 C for one hour, re-dried at roomtemperature and tested as in Example V. The results of these tests aregiven in Table X.

TABLE X Prevulcanized Untreated latex latex Modulus (kg/cm) at extensionof:

100% 7 7 300% 7 6 500% 7 4 Elongation-atbreak (96) l600 I600 Tensilestrength (kg/cm) 20 9 The test-pieces from the untreated latex flowedand yielded, whereas the test-pieces from the prevulcanized latex didnot flow and snapped at the elongation-atbreak stated.

EXAMPLE XIII To illustrate further the range of inorganic activatorswhich may be used in the invention, the untreated latex of Example V wastreated with the materials stated in Table XI. In each case theactivator was added in aqueous medium and dried films were prepared fromthe resulting prevulcanized latex and tested as in Example V. Theresults of these tests are given in Table XI, in which EB represents theelongation-at-break and TS denotes the tensile strength of the driedfilm.

TABLE XI Properties Additions per 1 kg of untreated latex of dried film.Activator lOO-volume Hp, EB (11) TS 10 ml 5% sodium stannate 50 ml l60026' 20 ml saturated sodium borate (saturated at 25C) 50 ml [330* 33 20ml 5% lithium chloride 40 ml I560 27 ml sodium pervanadate 60 ml 120 29ml l0% potassium bicarbonate 50 ml l600 I7 ml 5% sodium metasilicate 50ml l600 l I (plus l5 ml 10%KOH) V 20 ml 5% sodium aluminate ml 530 I7Modulus at l600% elongation.

These results show a marked improvement over the properties of driedfilms prepared from the untreated latex. The test-pieces from theprevulcanized latices did not flow plastically.

EXAMPLE XIV 100 g of a 41 percent total solids latex, pH 11.2, of anethylene/propylene/dicyclopentadiene terpolymer containing 26 percentdicyclopentadiene were treated with 1 ml of 5 percent sodium tungstatesolution and 2 ml of IOU-volume hydrogen peroxide at room temperature(about 20 C). Three days later dried films were prepared from both theresulting prevulcanized latex and the untreated latex and tested as inExample V. The results of these tests are given in Table XII.

TABLE XII Prevulcanized Untreated latex latex Modulus (kg/cm) atextension of:

I00% I l 8 300% 27 20 Elongation-at-break 460 460 Tensile strength(kg/cm) 58 34 EXAMPLE XV One litre of a carboxylated styrene/butadienerubber latex containing 54 percent total solids (trade name Politone1097) was treated with 10 ml of 5 percent sodium tungstate solution and50 ml of IOO-volume hydrogen peroxide at room temperature (about 20 C).Dried films were prepared from both the resulting prevulcanized latexand the untreated latex and tested as in Example V. The results of thesetests are given in Table XIII.

TABLE XIII Prevulcanized Untreated latex latex Modulus (kg/cm) atextension of: 8 7 300% l0 I0 500% l6 l5 Elongation-at-break (96) 980lOlO Tensile strength (kg/cm) 58 4| EXAMPLE XVI TABLE XIV PrevulcanizedUntreated latex latex Tensile strength (kg/cm) 124 78Elongation-at-break (l) 1060 870 EXAMPLE XVII One litre of the untreatedstyrene/butadiene rubber latex of Example V was treated with 10 ml of 5percent sodium tungstate solution and 50 ml of l00-volume hydrogenperoxide at room temperature (about 20 C). The treated latex was blendedwith an equal weight of dry rubber of a natural rubber latex containing60 percent dry rubber, 0.2 percent ammonia and 0.25 percent boric acid(Blend A). A second blend was prepared (Control Blend) by mixing equalweights of dry rubber of the untreated latex of Example V and theuntreated natural rubber latex used in Blend A. One litre of the ControlBlend was treated with 50 ml of 100-volume hydrogen peroxide at roomtemperature (Blend B). Dried films were prepared from Blend A, theControl Blend and Blend B and tested as in Example V. The results ofthese tests are given in Table XV.

TABLE XV blend control Blend A blend B Tensile strength (kg/cm) 1 54 1435 Elongation-at-break (36) 1220 1080 l700 Modulus at [700% elongation.

The results in Table XV illustrate the improvement obtained by treatingthe latex blend (in which case the hydrogen peroxide-activator was boricacid present in the natural latex) or by treating the styre'ne/butadienerubber latex component prior to blending with natural latex.

EXAMPLE XVIII To 1 kg of the untreated latex of Example VI were added 10ml of 5 percent sodium tungstate solution and ml of l00-volume hydrogenperoxide. Further incremental additions of 10 ml of IOO-volume hydrogenperoxide were made on each of the following two days. The reaction wasperformed throughout at 31 C and the latex mixture was gently stirredfor seven hours after each hydrogen peroxide addition.-

Dried films were prepared from the resulting prevulcanized latex andtested as in Example V. The results of these tests are given in TableXVI.

TABLE XVI Modulus (kg/cm) at extension of:

100% 7 300% 8 500% 10 Elongationat-break (96) l 100 Tensile Strength(kg/cm) 30 EXAMPLE XIX One kg of a 40 percent total solids latex of astyrene/- butadiene rubber containing 24 percent styrene by mass (tradename Pliolite 2108) was treated with 25 ml of 100-volume hydrogenperoxide and ml of saturated sodium borate solution at room temperature(about 20 C). The following day the resulting prevulcanized latex wascompounded as shown in Table XVII and water was added to adjust thetotal solids content to 20 percent.

TABLE XVII Parts by weight y) Prevulcanized polymer latex 100 Resorcinoll1 Formaldehyde (37% aqueous solution) 6 Sodium hydroxide (10% aqueoussolution) 0.6

The compounded latex was maturedfor 24 hours at 23 C. Nylon cord (2/1260denier) was then dipped in TABLE XVIII Force required (kg/cm)Prevulcanized latex 15.5

Untreated styrene/butadiene rubber latex l0.8 Untreated vinylpyridineterpolymer latex 14.9

EXAMPLE XX 4 kg of the untreated styrene/butadiene rubber latex ofExample V were treated with 40 ml of 5 percent sodium tungstate solutionand 240 ml of lO0-volume hydrogen peroxide with gentle stirring at roomtemperature (about 20 C). The following day 50 ml of 10 percentpotassium hydroxide solution were added to the resulting prevulcanizedlatex which was then compounded as shown in Table XIX.

TABLE XIX Parts by weight y) Prevulcanized polymer latex Natural rubberlatex l0 Potasium hydroxide (10% aqueous solution) 1 Titanium dioxide(60% aqueous dispersion) l0 5 Zinc oxide (50%(fiueousdispersion) TrimeneBase (5 aqueous solution) I The natural rubber latex contained 60percent dry rubber and 0.7 percent ammonia,

The compounded latex was used in the process for the production ofrubber tape described in British Pat. Specification No. 957,014. Thelatex layer on the belt coagulated within 25 seconds and the tape soformed had sufificient wet gel strength to be separated with ease fromthe belt.

The untreated latex was also compounded as shown in Table XIX and usedin the process of British Pat. Specification No. 957,014 under identicalconditions. In this case the latex layer on the belt took 60 seconds tocoagulate and the tape so formed had such poor wet gel strength that ittore easily while attempting to separate it from the belt.

EXAMPLE XXI One kg of a 44 percent total solids latex of a styrene/-butadiene rubber containing 46 percent styrene by mass (trade namePolystar Latex IV) was treated with 10 ml of 5 percent sodium tungstatesolution and 20 ml of -volume hydrogen peroxide at room temperature(about 20 C). Dried films were prepared from both the resultingprevulcanized latex and the untreated latex, in each case after theaddition of one part by weight of potassium oleate per 100 parts byweight of rubber, and

tested as in Example V. The results of these tests are given in TableXX.

EXAMPLE XXII To 43.75 kg of the untreated styrene/butadiene rubber latexof Example V were added 450 g of percent sodium tungstate solution and1,810 ml of IOO-volume hydrogen peroxide. The mixture was gently stirredfor 28 hours during which its temperature was 18: 2 C.

590 ml of 10 percent potassium hydroxide solution were added to theresulting prevulcanized latex.

For the preparation of dipped articles, the treated latex was compoundedas shown in Table XXI.

TABLE XXI Parts by weight o Prevulcanized polymer latex 50 Naturalrubber latex 50 Potassium hydroxide (20% aqueous solution) I Sulphur(50% aqueous dispersion) l 2,2methylene-bis(4-ethyl-6-t-butylphenol)(50% aqueous dispersion) 1 Titanium dioxide (60% aqueous dispersion) l0Hepteen Base (30% aqueous emulsion) 0.05 Zinc salt ofmereaptobenzthiazole (50% aqueous dispersion) l Zincdibutyldithiocarbamate (50% aqueous dispersion) 0.1 Zinc oxide (50%aqueous dispersion) 3 The natural rubber latex contained 60 percent dryrubber and 0.7 percent ammonia. Hepteen Base is a condensation productof heptaldehyde and aniline.

A metal balloon former was dipped into a coagulant solution consistingof 10 parts by weight of calcium nitrate tetrahydrate per 90 parts byweight of isopropanol and the deposit was dried. The former was dippedinto a bath containing the compounded latex of Table XXI, slowlywithdrawn from the bath and re-immersed in the coagulant solution for 30seconds. The coagulated film on the former was washed and dried. Theballoon was removed from the former without dificulty and was free fromcracking. In a second experiment, the dried balloon on the former afterbeing heated in steam at 100 C for 30 minutes was also found to be freefrom crack- For comparison, the untreated latex was compounded as shownin Table XXI and evaluated in identical manner to the prevulcanizedlatex. In the: case of the untreated latex, the dried balloon wascracked and could not be removed from the former without tearing, andcracking was more severe after heating in steam.

EXAMPLE XXIII To 4"k g of the untreated styrene/butadiene rubber latexof Example V were added 90 ml of saturated sodium borate solution and 80ml of IOO-volume hydro- Moulded foam rubber samples were prepared fromthe resulting treated latex using the formulation shown in Table XXII.

TABLE XXII Parts by weight (dry) Treated styrene/butadiene rubber latexSulphur (50% aqueous dispersion) 22,2-methylene-bis(4-ethyl-6tbutylphenol) (50% aqueous dispersion) l Zincsalt of mercaptobenzthiazole (50% aqueous dispersion) 1.5 Zincdiethyldithiocarbamate (50% aqueous dispersion) 0.5

Ammonia (28% aqueous solution) equal to 0.05% N H calculated on thelatex mixing.

Zinc oxide (50% aqueous dispersion) 3 Trimene Base (50% aqueoussolution) 1 Sodium silicofluoride (30% aqueous dispersion) 2 The zincoxide, Trimene Base and sodium silicofluoride were added aftermechanically foaming the latex and were thoroughly stirred in. The foamwas poured into the molds measuring 8.5 X 6 X 3 cm and covered by a lid.It gelled 5 minutes after the addition of the sodium silicofluoride, theair temperature being 29 C. Seven minutes after gelling, the moulds weretransferred to an oven and heated in steam at l00 C for 30 minutes. Themoulds were then immersed in cold water and the foam rubber samples wereremoved, washed in cold water, passed through rubber-covered rollers toexpel most of the water and dried in air at 55 C for 16 hours. Thecellular structure of the samples was excellent.

Five frothings were carried out to produce foam rubber samples ofdifierent density. Two samples from each frothing were tested fordensity and modulus at 40 percent compression and then one sample fromeach frothing was cut into four test-pieces with the same dimensions forthe measurement of tensile strength and elongation-at-break. Thecompression modulus was determined after compressing the sample by atleast 60 percent 20 times. The tensile strength and elongationat-breakwere measured at a rate of extension of 50 cm per minute.

The average density and average compression modulus obtained from eachfrothing were graphed and by interpolation the density at a compressionmodulus of 75 g/cm was found to be 0.112 g/cm. The average tensilestrength and the average elongation-at-break obtained from each frothingwere plotted against the corresponding density and the tensile strengthand elongation-at-break at a density of 0.112 g/cm were found to berespectively 610 g/cm and For comparison, the untreatedstyrene/butadiene rubber latex of Example V was compounded as shown inTable XXII except that it was necessary to increase the amount of sodiumsilicofluoride from 2 to 3 parts by weight in order to obtain a gellingtime of 6 mins. (at 27 C), and foam rubber samples were prepared, testedand evaluated in identical manner to the treated latex. The cellularstructure of the samples was very good. The evaluation gave for acompression modulus of 75 g/cm a foam density of 0.123 g/cm", a tensilestrength of 520 g/cm and an elongation-at-break of percent.

Thus the foam rubber prepared from the treated latex showed a weight(density) saving of 9 percent, corresponding improvement in tensilestrength of 17 percent and a corresponding decrease inelongation-atbreak of only one-ninth, with respect to the foam rubberprepared from the untreated latex, which differences are consistent withthe prevulcanized nature of the treated latex.

EXAMPLE XXIV To 2 kg of the untreated styrene/butadiene rubber latex ofExample V were added 40 ml of saturated sodium borate solution and 40 mlof lOO-volume hydrogen peroxide and the mixture was gently stirred for 3hours at 30 C.

The resulting treated latex was used in a latex/resin adhesive forbonding canvas to canvas, the adhesive being dried for 20 minutes at 120C. Part of the canvas/canvas composite was aged for 100 hours at 70 Cwhile the remainder was kept (unaged) at room temperature. The averagepeel strengths of the unaged and aged samples were then determined, inpounds force, on 2-inch strips at 2 inches per minute. For comparison,the untreated styrene/butadiene rubber latex was used and tested inidentical manner. The results of the tests are given in Table XXIII.

TABLE XXIII Treated Untreated (lb force) (lb force) Unaged 12.2 4.7 AgedI hours at 70C. [7.6 l2.7

EXAMPLE XXV To 4 kg of the untreated styrene/butadiene rubber latex ofExample V were added 80 ml of 5 percent lithium chloride solution and 80ml of 100-volume hydrogen peroxide. The mixture was gently stirred for 3hours during which its temperature was maintained at 30 C. The followingday the pH of the treated latex was adjusted to 10.0 (which was the pHof the untreated latex) by addition of percent potassium hydroxidesolution. Foam rubber was prepared from the resulting treated latexusing the formulation shown in Table XXIV.

TABLE XXIV Parts by weight y Treated styrene/butadiene rubber latex 100Zinc oxide (50% aqueous dispersion) 3 2,2'-methylene-bis(4-etl'iyl-6-tbutylphenol (50% aqueous dispersion) l Trimene Base (50% aqueoussolution) 0.5 Diisocyanate (trade name Suprasec DN) 10 Sodiumsilicofluoride (30% aqueous dispersion) 3 The diisocyanate and sodiumsilicofluoride were added after mechanically foaming the latex to fivetimes its original volume and were well stirred in. The foam was pouredinto a mould 1 cm deep and scraped level. It gelled 5 minutes after theaddition of the sodium silicofluoride, the air temperature being 23 C.Ten minutes after gelling, the foam was removed from the mould and driedin air at 50 C for 16 hours. The sample had an excellent cellularstructure and recovered from finger indentation within 5 seconds.

For comparison, the untreated styrene/butadiene rubber latex of ExampleV was compounded as shown in Table XXIV except that 2 parts by weight ofsodium silicofluoride, instead of 3 parts by weight, were used to obtaina gelling time of 5 minutes (at 23 C), and foam rubber was prepared inidentical manner to the treated latex. In this case, the foam wasremoved from the mould with difficulty, 10 minutes after gelling, andthe dried sample still had not recovered 5 hours after fingerindentation.

EXAMPLE XXVI One kg of a 50 percent total solids latex of a styrene/-butadiene rubber containing 50 percent styrene by weight (trade namePolitone K.815) was treated with Y 10 ml of 5 percent lithium chloridesolution and 20 ml of lOO-volume hydrogen peroxide at room temperature(about 20 C).

For evaluation as a carpet backing latex, the resulting Thickening agent(10% aqueous solution)" l Trade name Vulcastab I-IS "Trade name ViscalexAH l0 The compounded latex, which had a total solids content of 69percent, was spread on the back of tufted carpet at the rate of 1,030 g(wet weight) per square metre and dried at C for 20 minutes. Theresulting backed carpet had excellent handle and excellent resistance tocracking.

For comparison, the untreated styrene/butadiene rubber latex wascompounded as shown in Table XXV and the compounded latex applied to thesame tufted carpet in identical manner to the treated latex. In thiscase, the resulting backed carpet had good handle and good resistance tocracking, i.e., was less advantageous than the carpet backed with thetreated latex compound.

Having now described our invention what we claim is:

l. A method for the production of a prevulcanized latex of a rubberypolymer having improved tensile properties which comprises treating anunsaturated polymer having aliphatic olefinic double bonds in an aqueousmedium with hydrogen peroxide together with a hydrogen peroxideactivator which does not encourage the decomposition of the hydrogenperoxide to produce molecular oxygen under the conditions of thetreatment, said activator being selected from the group consisting ofinorganic and organic compounds which yield a compound selected from thegroup consisting of per-acids and per-salts by reaction with hydrogenperoxide in aqueous medium.

2. A method according to claim 1 in which the hydrogen peroxide isemployed as an aqueous solution of concentration 5 to 65 per cent bymass.

3. A method according to claim 1 in which the activator is a compoundselected from the class consisting of acidic and amphoteric inorganicoxides and salts thereof.

4. A method according to claim 1 in which the activator is a compoundselected from (a) salts of sodium and potassium being molybdates,tungstates, stannates, borates, pervanadates, metasilicates, aluminatesand bicarbonates, (b) lithium chloride and (c) boric. acid.

5. A method according to claim 1 in which the amount of activatoremployed is at least l millimole per mole of hydrogen peroxide.

6. A method according to claim 1 in which the activator is selected fromthe class consisting of formic acid, formaldehyde and fluoroacetic acid.

7. A method according to claim 1 in which the said treatment isperformed under conditions which minimise loss of oxygen.

8. A method according to claim 1 in which the said treatment isperformed under acidic conditions.

9. A method according to claim 1 in which a complexing agent for metalions is present during the treatment.

10. A method according to claim 1 in which the disodium salt ofethylenediamine tetra-acetic acid is pres ent during the treatment. i

11. A method according to claim 1 in which the unsaturated polymer isselected from the class consisting of styrene/butadiene copolymers,ethylene/propylene/- diene terpolymers, polybutadienes,polychloroprenes, styrene/butadiene/vinylpyridine terpolymers,butadiene/acrylonitrile copolymers, isoprene/acrylonitrile copolymers,carboxylated styrene/butadiene copolymers and natural rubber.

12. A prevulcanized polymer lateir when produced by a method accordingto claim 1.

13. A method according to claim 1, wherein said treatment is conductedat room temperature.

14. A method according to claim 1, wherein said treatment is conductedat a temperature of from about 16 to about 31 C.

2. A method according to claim 1 in which the hydrogen peroxide isemployed as an aqueous solution of concentration 5 to 65 per cent bymass.
 3. A method according to claim 1 in which the activator is acompound selected from the class consisting of acidic and amphotericinorganic oxides and salts thereof.
 4. A method according to claim 1 inwhich the activator is a compound selected from (a) salts of sodium andpotassium being molybdates, tungstates, stannates, borates,pervanadates, metasilicates, aluminates and bicarbonates, (b) lithiumchloride and (c) boric acid.
 5. A method according to claim 1 in whichthe amount of activator employed is at least 1 millimole per mole ofhydrogen peroxide.
 6. A method according to claim 1 in which theactivator is selected from the class consisting of formic acid,formaldehyde and fluoroacetic acid.
 7. A method according to claim 1 inwhich the said treatment is performed under conditions which minimiseloss of oxygen.
 8. A method according to claim 1 in which the saidtreatment is performed under acidic conditions.
 9. A method according toclaim 1 in which a complexing agent for metal ions is present during thetreatment.
 10. A method according to claim 1 in which the di-sodium saltof ethylenediamine tetra-acetic acid is present during the treatment.11. A method according to claim 1 in which the unsaturated polymer isselected from the class consisting of styrene/butadiene copolymers,ethylene/propylene/diene terpolymers, polybutadienes, polychloroprenes,styrene/butadiene/vinylpyridine terpolymers, butadiene/acrylonitrilecopolymers, isoprene/acrylonitrile copolymers, carboxylatedstyrene/butadiene copolymers and natural rubber.
 12. A prevulcanizedpolymer latex when produced by a method according to claim
 1. 13. Amethod according to claim 1, wherein said treatment is conducted at roomtemperature.
 14. A method according to claim 1, wherein said treatmentis conducted at a temperature of from about 16* to about 31* C.